[KaVir]

I adapted my card game entry into a turn-based war game, and also considered using it for a social combat system. In theory I could even have used it for the main combat system. I've used other types of "minigame" for other aspects of the mud, such as lockpicking, alchemy, etc. I know other muds which do the same sort of thing for crafting, gathering resources (such as fishing and mining), and so on.

Card games are simply a type of game system. It's the way you use them that determines how much they add much to the MUD.